1. Field of the Invention
The present invention relates to a development apparatus in an image forming apparatus which visualizes an electrostatic latent image formed on an image bearing member with developer including toner in an electrophotographic system or an electrostatic recording system, in particular, related to a development apparatus mounted on an image forming apparatus.
2. Description of the Related Art
Conventionally, in an image forming apparatus utilizing an electrophotographic system, an electrostatic latent image formed on a photosensitive member as an image bearing member is visualized as a toner image with toner in developer by utilizing a development apparatus.
The most popular development apparatus is constituted with a developer container to accommodate developer, a conveying member to convey developer in the developer container while agitating and mixing, a developer bearing member to bear and convey developer to an opposed part of a photosensitive member, and a thickness restriction member to restrict developer quantity at the developer bearing member.
Here, the development apparatus utilizing dual-component developer containing nonmagnetic toner and magnetic carriers, for example, is described. The developer accommodated in the developer container is agitated and mixed by a conveying screw as a conveying member within the developer container. The developer is charged with frictional electrification during the process of the agitating and mixing. The charged developer is borne mainly with magnetic force at a developing sleeve as the developer bearing member having a magnet as magnetic field generating unit arranged at the inside thereof. The developing sleeve is rotatably arranged at a position opposed to the photosensitive member. The developer is conveyed to a developing area being the opposed part of the photosensitive member according to rotation of the developing sleeve and used for developing. In the developing area, the toner in the developer is transferred to an electrostatic latent image formed on a surface of the photosensitive member with developing bias applied to the developing sleeve, so that a toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive member.
In such a development apparatus, a restriction blade as the thickness restriction member is generally arranged so as to be opposed to a circumferential surface of the developing sleeve via a predetermined gap. As the restriction blade, various proposals such as a magnetic plate, a nonmagnetic plate, a combination thereof, and an elastic member are performed and actualized as well. When the developer borne at the developing sleeve is conveyed to the developing area, the quantity of the developer conveyed to the developing area is adjusted to be restricted during a process of passing through a gap between the developing sleeve and the restriction blade, so that stable quantity thereof is supplied.
With the development apparatus performing the thickness restriction of developer borne at the developing sleeve surface by the restriction blade, there may be a case that following problems occur.
FIG. 12 is a sectional view schematically illustrating a state of dual-component developer at the upstream side of the restriction blade position when utilizing dual-component developer known from the past. The developer gathered up to the surface of a developing sleeve 128 is borne at a surface of the developing sleeve 128, and then, conveyed to the vicinity of the upstream side in the developer conveying direction of the restriction blade position. The developer conveyed to the vicinity of the upstream side of the restriction blade 130 is accumulated once, and then, a part of the developer passes and is conveyed to the developing area having the thickness thereof restricted at the position of the gap between an edge of the restriction blade 130 and the surface of the developing sleeve 128. Meanwhile, the remaining developer which cannot pass through the gap is accumulated at the next upstream part of the restriction blade 130 and composes a developer non-flowing layer. In this manner, a developer flowing layer being conveyed corresponding to the rotation of the developing sleeve 128 and the developer non-flowing layer banked by the restriction blade 130 are formed at the upstream position of the restriction blade 130.
When the developer flowing layer and the developer non-flowing layer are formed as described above, the developer flowing layer rubs with the developer non-flowing layer at the boundary surface thereof. Consequently, in the case of the dual-component developer, toner is separated from carriers. Then, the separated toner is to be in a fixation-like state at the boundary surface due to friction heat by rubbing, so that a toner layer is formed. Such a toner layer grows with lasting usage and interferes with the gap between the restriction blade 130 and the developing sleeve 128. Accordingly, the quantity of developer passing through the gap is decreased. Consequently, the developer quantity conveyed to the developing area fluctuates and a problem such as darkness fluctuation occurs.
As countermeasures against the above problem, it is effective for resolving the problem to decrease developer quantity supplied to the restriction blade and lessen the developer non-flowing layer as reducing accumulation at the restriction blade as less as possible. However, when quantity of the developer supplied to the restriction blade is decreased, there is apt to arise a new problem that quantity of the developer passing through the gap becomes unstable. Therefore, a certain lump quantity of developer is required to exist at the upstream side of the restriction blade. Accordingly, it is difficult to completely eliminate occurrence of the developer non-flowing layer.
In Japanese Patent Laid-Open No. 5-035067, it has been proposed to arrange, at the next upstream side of the restriction blade, a cylinder-shaped toner conveying member which constantly rotates having a consistently constant gap with a developing sleeve in order to prevent forming of the developer non-flowing layer.
In Japanese Patent Laid-Open No. 5-035067, it is described that occurrence of the developer non flowing layer can be prevented. However, bearings to support the toner conveying member and drive unit are required, so that structure complication and cost increase are unavoidable. Further, since the toner conveying member is driven in the opposite direction at a position opposed to the developer bearing member, there may be a risk that developer rapidly deteriorates since strong stress is to be applied to the developer. In addition, in the case of high-speed rotation, there may be a risk that developer is melted and fixed due to generation of heat.
In Japanese Patent Laid-Open No. 2005-092061, a configuration to suppress forming of the developer non-flowing layer into a slight area by arranging a developer accumulation restriction member at a position where the developer non-flowing layer is apt to be formed as developer is accumulated.
However, in Japanese Patent Laid-Open No. 2005-092061, there may be a risk that a toner layer is formed against the developer flowing layer during lasting long usage and starts to disturb developer flowing when the developer non-flowing layer is formed even in the slight area.